Fuel pumps utilized for providing hydrocarbon fuels in liquid form to the carburetor or throttle body of an internal combustion system are usually powered by an electric motor in which the armature is mounted in the fuel pump body. These pumps must be capable of operating in a wide range of ambient temperatures.
The hydrocarbon fuels (gasoline and alcohol) have a relatively low boiling point. In certain geographical areas, the ambient temperatures may reach 110.degree. to 120.degree. Fahrenheit. The temperature in the fuel tank below the automotive vehicle may be even higher than this. Since these pumps are frequently mounted in the fuel tanks, there is a great likelihood that the fuel in the pump may vaporize. The pumps are usually positive displacement pumps and it is necessary that the entry to the pump chambers create a low pressure to draw fuel into the pumping chambers.
This reduced pressure alone may cause a change in state of the fuel from liquid to vapor at elevated temperatures and significantly reduce the efficiency of the pump. In another condition as, for example, when a vehicle has been operating and then the engine shut off for a period, the fuel line between the pump and the carburetor or other fuel mixing device is full of liquid fuel under pressure whereas the fuel in the pump can be completely vaporized due to the elevated temperature in the fuel tank and pump itself. Thus, when the engine is restarted, the pump is full of vapor and even the fuel in the entrance filter may be vaporized. The pump cannot, under these conditions, generate enough pressure to move the fuel in the pressurized fuel supply line.
It is an object of the present invention to provide a pump construction with a purging system which will enable the pump to operate under the conditions above described without an interruption of the fuel supply.
It has been previously known to provide a vapor bleed port in a pump at the high pressure area, this port being very small to avoid excessive loss of fuel during normal operation. Also various valving mechanisms have been used to expel vapor during the initial priming stage and to close when liquid fuel reaches the pump. These devices have, however, proved unreliable. For example, the small purge port at the high pressure area may clog with foreign particles and cease to function. In the valve mechanism type, the valves do not always open or close at proper times due to operating environmental conditions. In the present invention the purging is accomplished by establishing a relatively large purge port at a strategic location relative to the pump elements such that vapor will be expelled to the tank and liquid fuel will enter the pump to create the necessary pressure in the fuel line.
It is a further object to provide a purge port which is sufficiently large that it will be self-cleaning and not be clogged by dirt particles and yet will not affect the general efficiency of the pump. In addition, the enlarged purge port is located such that there is a wiping action by the pump elements which provides a self-cleaning function. Another feature lies in the fact that the pumping elements close the purge port part of the time so the efficiency of the pump is not materially affected. A still further object is the provision of a vapor purge system which avoids start delays when the pump is energized.
Other objects and features of the invention will be apparent in the following description and claims in which the invention is described together with details to enable persons skilled in the art to practice the invention, all in connection with the best mode presently contemplated for the invention.